Most of the 147 victims of a terror attack on a university on Thursday were lined up and shot, a senior Kenyan government confirmed yesterday.

Some students were killed as they spoke to their parents on the telephone, having been ordered to call with messages from the gunmen that their aim was to force Kenyan troops to leave Somalia, the source added.

"This is the level of depravity that we are dealing with. It is something beyond the comprehension of anyone normal like you or I," the source added.

"These are not people who can be reasoned with, only force can stop them."

The suicide vest-clad gunmen, whom the Somali terror group al-Shabaab claimed as their own after they stormed Garissa University in north-eastern Kenya, warned students of further attacks to come, survivors revealed.

Maureen Manyengo, a 21-year-old Christian from western Kenyan who was training to be a teacher, described how she hid inside her wardrobe after seeing several friends killed.

She said the terrorists also told the cowering students: "We are not bad guys, we are just here to make your Easter holiday better."

Reuben Nyaora, an aid worker who was among the first to enter the university after the terrorists' final clash with Kenyan special forces late on Thursday afternoon, described seeing women rise from among the corpses covered in blood but unscathed.

"I have seen many things, but nothing like that," said Mr Nyaora. "There were bodies everywhere in execution lines, we saw people whose heads had been blown off, bullet wounds everywhere. It was a grisly mess."

So far, 147 people have been confirmed dead in Kenya's worst terror attack for two decades, but officials admit that the death toll could climb higher still as piles of bodies are recounted.

Questions remained about how the 15-hour siege ended and how the death toll jumped from 70 in the afternoon to 147 just over an hour later. Some Kenyans accused the government of failing to take sufficient security precautions. The attack happened six days after Britain advised "against all but essential travel" to parts of Kenya.

Kenya's interior minister confirmed the gunmen had been strapped with explosives and blew up "like bombs".